Internally vibrated roller cutter apparatus for cutting earth and rock

ABSTRACT

A roller tool, such as a chisel, especially for mining in which vibratory forces are developed inside the tool in the working direction thereof for enhancing the cutting effect thereof on a formation to which the tool is presented.

UnIted States Patent [151 3,695,72 1 Jungel Oct. 3, 1972 [54] INTERNALLY VIBRATED ROLLER [56] References Cited CUTTER APPARATUS FOR CUTTING EARTH AND ROCK UNITED STATES PATENTS [72] Inventor: Heinrich Jungel, Rhcinhausen, Ger- "m 3,082,668 3/1963 Matson ..94/ v [73] Assignee: Fried, Krupp Gcsellschaft mit 3,151,912 10/1964 Herrmann ..299/34 beschrankter Haftung, Essen, Ger- 3,544,075 12/1970 Sugden 175/55 X 22 Pl d 2: 3 l 7 FOREIGN PATENTS OR APPLICATIONS 1 l 9 0 1,205,024 11/1965 Germany ..175/ 1 1 pp ,398 347,785 1/l922 Germany ..173/49 Primary Examiner-Ernest R. Purser [30] Foreign ApphcatIon Priority Data y a1 ter Becker Oct. 24, 1969 Germany ..P 19 53 550.3

ABSTRACT [52] Cl 4 252 A roller tool, such as a chisel, especially for mining in Int Cl 4 i 25410 which vibratory forces are developed inside the tool in a o e e I 1 n v e I e u I e I I e n e I l e I e I I e o e II f 58 Field of Search ..299/14, 34, 86, 69, 40, 37; the wmkmg dlrecm" themf enhancmg the /55, 56, 96; 173/49; 74/61; 172/40; 37/D1G. 18; 94/50 V cutting effect thereof on a formation to which the tool is presented.

1 1 Claims, 6 Drawing Figures INTERNALLY VIBRATED ROLLER CUTTER APPARATUS FOR CUTTING EARTH AND ROCK comprises vibrators which subject the roller chisel to oscillations parallel to the direction of movement of the bearings.

Driving devices of this type are known in the art. According to these driving devices, the bearing bodies of the roller chisels are mounted for instance at the lower ends of rods which are displaceably guided in vertical bores of the tool carrier against the thrust of springs. For each individual roller chisel there is provided an unbalance vibrator which is mounted on a platform at the upper end of the respective rod, which end protrudes beyond the tool carrier. According to another heretofore known working device of the above mentioned type, a plurality of unbalance vibrators are arranged on the tool carrier which is displaceably guided by a shank in vertical direction while a set of weights, through the intervention of springs, acts upon the upper end of the shank.

While with such feeding devices, due to the employment of the unbalance vibrators, it is realized over other customary roller chisel driving devices that the feeding forces to be transferred to the tool carrier and also the torque required for turning the tool carrier are considerably reduced and consequently the wear at the tool edges is reduced and the device can be built lighter, these known driving devices have the drawback that the bearing of the roller chisel is subjected to extremely strong push stresses. This fact results in damage to the bearings and consequently to an early failure of the device.

It is, therefore, an object of the present invention to provide a working device with roller chisels, especially a driving device for drifts, tunnels, shafts, and the like which will combine the above mentioned advantages inherent to the employment of vibrators for advancing devices, with roller chisels, without encountering the above mentioned drawbacks.

These objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 diagrammatically illustrates a vertical axial section through a roller chisel and a portion of the tool carrier according to the present invention.

FIG. 2 represents a section taken along the line II-II of FIG. 1.

FIG. 3 is a section similar to that of FIG. 2 for two different positions of an unbalance mass. FIG. 4 is a vertical axial section through a roller chisel and a portion of the tool carrier according to a modification of the present invention.

FIGS. 5 and 6 illustrate roller chisels and the structural elements carrying the same, according to a third and fourth embodiment respectively of the present invention.

The working device according to the present invention is characterized primarily in that the vibrators are mounted in the interior of the hollow roller chisels and act upon the same while bypassing the bearings. Preferably, for this purpose, vibrators known per se are employed which comprise housings with cylindrical roller paths provided in the interior of said housings for roller bodies serving as unbalancing mass, said housings being formed by the roller chisels. This may be realized in a manner known per se in such a way that the roller path of a vibrator is formed by the circumferential surface of a shaft which extends through the housing and is fixedly connected thereto. Furthermore, as known per se, the roller body forms a circular ring and has its bore, the diameter is greater than the diameter of the shaft surrounded by the latter. However, it is also possible that the roller path of a vibrator is formed by the circumferential surface of the hollow chamber of the housing. In this connection, expediently similar to the known vibrators, the roller movement of the roller body on the roller path is produced by compressed air or the like introduced into the housing, i.e., into the interior of the roller chisel. The employment of compressed air for driving unbalance masses within the roller chisel brings about the particular advantage that a cooling effect is obtained when the compressed air expands. This cooling effect has a favorable effect upon the roller chisel and the bearings therefor. Moreover, the air which leaves the roller chisels can be used for lubricating purposes and for protecting the bearings against dust, or the like. The employment of compressed air, especially in connection with shaft drilling devices furnishes the possibility to blow the ore bottom within the working range of the roller chisels free from loosened material by the air leaving said roller chisel. However, the unbalance masses, instead of being driven by compressed air, may also be driven in a different way, for instance, hydraulically.

In order to avoid harmful effects of the oscillations of the roller chisels upon the bearings therefor, and upon the guiding path of these bearings, expediently two or more roller paths each are arranged within said roller chisel for counter moving roller bodies, said roller paths being arranged adjacent to each other. The guiding paths of said bearings are so designed that they are able to offer as high a resistance as possible to any radial movement of oscillation of the roller chisel in a direction transverse to the direction of movement of the bearings, i.e., parallel to the working face. As a result thereof, with compressed air-driven vibrators it will be assured that the phase locations of the centrifugal forces of the roller bodies, which centrifugal forces rotate in counter current direction at the same frequency will automatically adjust themselves in such a way that in all positions of the roller bodies, the total of the centrifugal force components respectively located at a right angle with regard to the direction of movement of the bearings are at least approximately zero, which means that a centrifugal force directed toward the ore will be produced. Preferably, within the roller chisel there are provided adjacent to each other three or more roller tracks or roller paths for counter moving roller bodies in such a way that in all positions of the roller bodies, also the total of the moments exerted upon the roller chisel by the centrifugal force components respectively at a right angle to the direction of movement of the bearings, will at least approximately be zero.

In order to keep the oscillations produced by the vibrators within the roller chisel away from the tool carrier as much as possible, it is expedient to select the frequence of the oscillations of a roller chisel at least approximately equal to the fundamental frequency of the oscillation system which is formed by the masses taking part in the oscillating movement and by the springs between the pertaining bearings and the tool carrier. in this connection, it has proved advantageous that the working frequency of the vibrator will, only at an approximate tuning of the system in the above mentioned way, adjust itself automatically in conformity with the fundamental frequency and will follow also slight changes in the fundamental frequency of the system. Fundamentally, however, the fundamental frequency of the system may also be selected much lower than the working frequency of the vibrator.

Inasmuch as with heretofore known non-balance vibrators the non-balance masses rolling on the rolling paths have no bearings, a compact construction and thus relative high frequencies of the oscillations and high centrifugal forces can be realized. This is of great importance for the driving devices with roller chisels according to the present invention. Of particular advantage for a driving device according to the invention is the extremely favorable starting behavior of the above mentioned known unbalance vibrators. In this connection it should be noted that it makes possible of a fast control of the air supply to the individual roller chisels in such a way that in each instance only those roller chisels are subjected to oscillations which are in sufficiently intimate contact with the ore. Furthermore, the power absorption and output of the compressed air operated vibrators automatically adapt themselves to the respective ore resistance, which fact contributes to a saving of the entire system.

Referring now to the drawings in detail, and more specifically to FIGS. 1 and 3, the hollow roller chisel 1 shown therein is passed through by a shaft 2 arranged co-axially with regard to the roller chisel l. Shaft 2 is fixedly connected to the roller chisel 1. The ends of shaft 2 protrude at both sides of the end walls 3 of the roller chisel l and are located in bearings 4. These bearings form sliding bearings, but if desired, also antifriction bearings may be employed instead.

The bearings 4 are located in guiding bodies 5 which, by means of upwardly extending cylindrical studs 6 are displaceably guided in vertical bores of the tool carrier 7. Tool carrier 7 is, in a manner known per se, rotatably journalled on the frame, for instance, of a shaft driving machine so as to be rotatable about the shaft axis. The drives acting upon the tool carrier 7 for turning and for the feed may be realized in any standard manner. Between the tool carrier 7 and below collars of the guiding body 5, which collars are arranged below said tool carrier 7, there are provided strong dish springs 8, by means of which, the roller chisel 1 is, by the tool carrier 7, pressed against the bottom 9 of the mine shaft. The springs 8 are preferably by counter springs 8a preloaded by nuts 6a. Within the scope of the present invention, the roller chisel may act upon the ore in any other arrangement, for instance, may press against the face (Ortsbrust) of a drift or tunnel to be driven. As far as the essence of the invention is concerned, it is immaterial how the individual roller chisels of the driving device are arranged with regard to each other. Depending upon the circumstances, they may be stepped in radial direction with regard to the axis of rotation of the tool carrier 7 and also in the direction of rotation of the tool carrier with regard to each other.

The roller chisel 1 has three cylindrical co-axial hollow chambers 10, 11, 12 which are separated from each other by partitions 13, 14 extending to the shaft 2. Arranged in the hollow chambers 10, 11, 12 there are provided three circular metallic rings l5, l6, 17 which form the unbalance masses. These unbalance masses have their end faces in close engagement with the end faces of the hollow chambers l0, ll, 12. They have the same outer diameter and by means of the walls defining their bores extend around the shaft 2. The bores of the three rings have the same diameter, which is greater than the diameter of the shaft 2. The rings 15 and 17 have the same width. They are half as wide as the ring 16.

The shaft 2 has one end provided with an extension or stud 18 which protrudes beyond a guiding body 5. This guiding body is, through the intervention of seals 19, surrounded by an annular body 20 which is secured against rotation. Body 20 comprises an annular chamber which, through the intervention of a nipple, is connected to a compressed air feeding line 21 and through radial bores in stud l8 communicates with an axial bore 22 of shaft 2. This bore 22, which is closed at the end of the stud 18, extends into the region of the unbalance rings l7, l6, l5. Bore 22 communicates through radial slots 23, 24, 25 in shaft 2 with the hollow chambers 10, 11 and 12, respectively. In these slots, guiding members 26, 27, 28 are guided which, by means of their end faces closely engage the end faces of the hollow chambers 10, ll, 12 as well as the end faces of slots 23, 24, 25, which end faces are flush with the end faces of the hollow chambers 10, ll, 12. Furthermore, said sliding members 26, 27, 28 are in line contact with the cylindrical surfaces of the bores of the rings l5, 16, 17. The sliding members are at one side thereof provided with grooves 29 through which compressed air may pass from the axial bore 22 into bores of rings 15, l6, 17. In the vicinity of the opposite side of slide members 26, 27, 28, the end walls 3 and the partitions l3, 14 are provided with radially extending grooves 30, which on one hand lead into the bores of the rings l5, 16, 17, and on the other hand lead into the hollow chambers l0, ll, 12 close to the circumferential surfaces thereof and, more specifically, outside the rings l5, 16, 17. In this way, the radial grooves 30 are, through the intervention of passages 31, 32, provided in end walls 2 and in end walls 13, 14 respectively, in communication with the atmosphere.

According to the embodiment illustrated in FIGS. 1 and 2, the three rings l5, 16, 17 have the same position with regard to the shaft 2. The said three rings engaging the cylindrical circumferential surface of shaft 2 at the highest mantle line 33 of said circumferential surface. Accordingly, the center line 34 of the rings, i.e., the line of gravity thereof is located below the center line 35 of shaft 2. It is assumed that the roller chisel 1 occupies such rotary position that the radial slots 23, 24, 25

of shaft 2 extend from the axial bore 35 in a vertical direction downwardly. Consequently, the slides divide that portion of the bore of each of said three rings which is left free by shaft 2, into two sections 36, 37 which at the top by the engagement of the rings with the shaft 2 are separated from each other at the mantle lines 33.

From the feeding line 21, compressed air flows into the chambers 36 through the annular bodies and the axial bore 23 as well as through the slots 23, 24, 25 and the grooves 29. The compressed air has the tendency to increase these chambers whereby a rolling movement of the rings 15, 16, 17 is brought about. This means that the mantle lines along which the rings 15, 16 and 17 engage the shaft 2, will move over the circumference of shaft 2 in such a way that the chambers 37 will be reduced. From these chambers, air passes through the radially extending grooves and passages 31, 32 into the atmosphere.

The rolling movement of the intermediate ring 16 is directed opposite to the rolling movements of the rings 15 and 17. This is due to the fact that the grooves 29 of the slide 27 when viewing the starting position of FIG. 2, are located on that side opposite to that of grooves 29 of slides 26 and 28, and that consequently also the radial groove 30 in the partition 13 is located on that side of the slide which faces away from grooves 29, in other words, when looking at FIG. 2 on the right-hand side of the there illustrated slide. The rotating speeds of all three rings 15, 16, 17 are the same. The center lines, for instance 34, of rings 15, 16, 17 will, during the rotation of the rings, move on circular cylinders, the center lines of which co-incide with the center line 35.

FIG. 3 shows the rings in a position which they occupy when said rings have rolled on the shaft to such an extent that the mantle lines 30', 32 along which the rings l5, l7, l6 engage the circumferential surface of shaft 2 have moved out by 45 from the starting position 33. The lines of gravity of the rings have moved into the positions designated with the reference numerals 34 and 34" respectively. In view of the eccentricity of these lines of gravity with regard to the center line 34 of shaft 2, centrifugal forces F and F occur in the rings. The directions of these centrifugal forces define together with the vertical line passing through the center line 35, angles of 45 each. These centrifugal forces F and F of the rings 15 and 17 having the same size, are of equal magnitude and their sum equals the centrifugal force F FIG. 3 shows the composition of the centrifugal force F and of the sum of the cen trifugal forces F and F of two horizontal components W and two vertical components L. The horizontal components W cancel each other out whereas the vertical components L add to each other. The total of the vertical components is the total force which is exerted upon the roller chisel 1 by the unbalance masses 15, 16, 17in their respective illustrated positions. Inasmuch as this force drives the cutting edges of the roller chisel downwardly into the ore 9, the ore will be blown up to a corresponding extent. In this connection, it is important that this force is, by rings l5, 16, 17 directly conveyed to the shaft 2 which is fixedly mounted in the roller chisel 1 while the bearings 4 are being by-passed. These bearings can follow freely the corresponding vertical oscillating movements of the roller chisel l, inasmuch as the studs 6 of the guiding bodies 5 are able to slide in the bores of the tool carrier 7. In order to assure that for purposes of accelerating and retarding of the masses comprising the bearings 4, in other words, the masses of the guiding bodies 5, as small forces occur in bearings 4 as possible, the said masses are kept as small as possible.

Since the horizontal components W in all positions of rings 15, 16, 17 cancel each other out and since the rings 15, 16 and 17 are arranged symmetrically with regard to the vertical transverse central plane 38 of the roller chisel 1, not only will the sum of the components W equal zero, but also the moments exerted by the components W upon the roller chisel 1 will cancel each other out. Consequently, the bearings 4 are not subjected to stresses by transverse forces resulting from the oscillations of the roller chisel 1. Furthermore, in view of the fact that the horizontal components W of the centrifugal forces and the moments thereof always cancel each other out and consequently no transverse forces occur in bearings 4 it will be avoided that such transverse forces exert torques upon the guiding bodies 5 and consequently exert stresses upon the studs 6 and the guiding bores therefore in the tool carrier 7.

During the operation of the roller chisel, the latter rolls in conformity with the rotary movement of the tool carrier 7 on the ore. According to FIG. 2, the advancing direction of shaft 2 is designated by the arrow A. Accordingly, the roller chisel 2 will, with regard to FIG. 2, rotate in a counterclockwise direction. This also applies to shaft 2 fixedly connected thereto, which shaft 2 rotates in bearings 4. Also the slides 26, 27, 28 and the radial grooves 30 take part in said rotary movement. The rolling movements of the compressed airdriven rings l5, l6, and 17 about shaft 2 are not affected by the said rotation. The speed of rotation of rings l5, l6, l7 greatly exceeds the circumferential speed of the roller chisel.

Unbalance-vibrators, as formed with the described embodiment of the invention by rings 15, 16, 17 and the hollow roller chisel 1 with shaft 2 are, as mentioned above, known per se. It is also possible to employ a different type of likewise known unbalance vibrators for the roller chisel. In this instance, the unbalance masses are formed by balls or circular cylindrical bodies which roll on circular cylindrical inner surfaces of the roller chisel. The drive for the rotary movements of these unbalance masses is likewise effected by compressed air which automatically is fed through the shafts of the roller chisels. However, in this instance, the compressed air is not controlled by slides or valves, but is, by nozzles in jets approximately tangential to the path of rotation directed toward the ball or cylinder-shaped unbalance masses.

It should be noted that the invention is not limited to embodiments in which the oscillations of the roller chisel are produced by unbalance masses rolling in the interior of the roller chisel.

FIG. 4 shows another embodiment of the present invention. According to FIG. 4, the roller chisel 40 is held in bearings of two guiding bodies 43 by means of hollow studs 41. The said guiding bodies 43, similar to the guiding bodies 5 of the first embodiment described above are vertically displaceably guided in the bores of the tool carrier 7 and rest from below against the tool carrier by means of preferably pre-loaded dish springs 8. In a hollow chamber 44 of the expediently divided roller chisel 40 there is provided a housing 45 with studs 46 which, on both sides, extend through bores of the hollow stud 41 toward the outside where they are rigidly connected to the guiding body 43. In the lower portion of housing 45 there is vertically displaceably guided a bolt 47, the rounded end of which, protrudes downwardly out of the housing 45 and into a groove 48 of the roller chisel 40. Above the bolt 47 and co-axial therewith there is displaceably guided an impact bolt 49 which is held in its illustrated elevated position by means of a spring 50. By compressed air, which is introduced through a passage 51 in housing 45 through one of the studs 46 into the chamber above the impact bolt 49, the latter is driven downwardly so that the impacts upon the bolt 47 with the result that the latter in groove 48 hits upon the roller chisel 40. The compressed air may, for instance, by means of a discharge conduit 52 which is released in the lowermost position of the impact bolt 49, in combination with spring 50 placed into oscillations so that the roller chisel 40 will, in the rhythm of said oscillations receive downward shocks by the bolt 47, in other words, will be subjected to oscillations for breaking up the ore 9.

These oscillation of the roller chisel are produced likewise while by-passing the bearings 42 so that the latter cannot be subjected to stresses by shocks in conformity with the roller chisel oscillations.

FIG. shows that the bearings of a roller chisel 1 which, in conformity with this invention, has vibrators 58 arranged in the interior thereof will not be located in vertically displaceable guiding bodies as is the case with the embodiment of FIGS. 1 4. Instead, a support 53 which comprises the bearings 54 of the roller chisel is arranged on a pivotable member 55 which is pivotally located below the tool carrier 7 on a support 56. The arrangement is such that the pivot axis 57 is parallel to the center line of bearings 54 and is arranged in spaced relationship thereto. This brings about that transverse forces O which occur as horizontal components of the centrifugal forces of unbalance masses, for instance, of a ring 58, in conformity with ring in FIGS. 1 3 are favorably absorbed by the bearings 59 of support 56. If such transverse forces did occur, for instance, with the embodiment of FIGS. 1 3, they would exert considerable bending moments with regard to the centers of the guiding bores so as to damage the same. This would occur in view of the great difference in height between the bearings 4 and the guiding bores for the studs 6 in the tool carrier 7. With the arrangement of FIG. 4 a greater strength is obtained in a direction transverse to the working direction as it is necessary for producing directed oscillations.

Springs 60, by means of which with the embodiment of FIG. 5, the bearing body 50 rests against the tool carrier are expediently located in a recess of the tool carrier above the bearing support 53. These springs are preloaded through the intervention of counter springs 61 and nuts 62.

According to FIG. 6, the rocker or oscillatable member 55 may be formed by a leaf spring 63 having one end connected to the tool carrier 7. This embodiment is simpler and can produce an even greater rigidity in strength in a direction transverse to the working direction.

It is, of course, to be understood that the present invention is, by no means limited to the particular showings in the drawings, but also comprises any modifications within the scope of the appended claims.

What is claimed is:

1. In a work tool head for working formations, especially earth and rock formations, as in mining and like operations; hollow roller cutter means for cutting engagement with a formation being worked, a work tool carrier, bearing means rotatably supporting said hollow roller cutter means, means resiliently supporting said bearing means on said work tool carrier, vibrator means for vibrating said hollow roller cutter means in the working direction thereof to augment the cutting action of the hollow roller cutter means, said vibrator means being unbalance mass means mounted inside said hollow roller cutter means and acting directly thereon, and means for driving said unbalance mass means in rotation thereby to develop vibrating forces on said hollow roller cutter means.

2. A work tool head according to claim 1 which includes a shaft extending axially through said hollow roller cutter means and fixed thereto, said mass means surrounding said shaft with radial clearance and rolling thereon when driven in rotation.

3. A work tool head according to claim 2 in which said shaft extends from both ends of said hollow roller cutter means and is rotatably supported by said bearing means.

4. A work too] head according to claim 1 in which said unbalance mass means rolls on the inside of said roller cutter means when driven in rotation.

5. A work tool head according to claim 1 which includes compressed air inlet means leading into said roller cutter means, and means for driving said mass means in rotation by compressed air supplied to said roller cutter means via said inlet means.

6. A work tool head according to claim I in which said mass means comprises at least two cylindrical mass elements in said roller cutter means adapted to rotate therein in opposite directions and at such phase relation to each other as to balance out vibrating forces developed on said roller cutter means which are at right angles to said working direction of said roller cutter means.

7. A work tool head according to claim I in which said mass means comprises three cylindrical masses in side by side relation in said roller cutter means with one mass rotating in one direction and the other two masses rotating in the opposite direction and with the phases of the masses being such that all vibrating forces developed on said roller cutter means which are at right angles to said working direction of said roller cutter means are balanced out.

8. A work too] head according to claim 1 in which the natural frequency of said mass means is approximately equal to the natural frequency of the weight of the roller cutter means and the bearing means therefor and the means suspending the roller cutter means from said carrier.

9. A work too] head according to claim 1 in which said means supporting said bearing means on said carrier comprises an arm which at one end engages said bearing means and at the other end is supported on said carrier.

10. A work tool head according to claim 9 in which said arm is a leaf spring and at said other end is fixed to said carrier.

1 l. A work tool head according to claim 9 in which said arm at said other end is pivotally supported on said carrier on an axis parallel to the axis of rotation of said roller cutter means. 

1. In a work tool head for working formations, especially earth and rock formations, as in mining and like operations; hollow roller cutter means for cutting engagement with a formation being worked, a work tool carrier, bearing means rotatably supporting said hollow roller cutter means, means resiliently supporting said bearing means on said work tool carrier, vibrator means for vibrating said hollow roller cutter means in the working direction thereof to augment the cutting action of the hollow roller cutter means, said vibrator means being unbalance mass means mounted inside said hollow roller cutter means and acting directly thereon, and means for driving said unbalance mass means in rotation thereby to develop vibrating forces on said hollow roller cutter means.
 2. A work tool head according to claim 1 which includes a shaft extending axially through said hollow roller cutter means and fixed thereto, said mass means surrounding said shaft with radial clearance and rolling thereon when driven in rotation.
 3. A work tool head according to claim 2 in which said shaft extends from both ends of said hollow roller cutter means and is rotatably supported by said bearing means.
 4. A work tool head according to claim 1 in which said unbalance mass means rolls on the inside of said roller cutter means when driven in rotation.
 5. A work tool head according to claim 1 which includes compressed air inlet means leading into said roller cutter means, and means for driving said mass means in rotation by compressed air supplied to said roller cutter means via said inlet means.
 6. A work tool head according to claim 1 in which said mass means comprises at least two cylindrical mass elements in said roller cutter means adapted to rotate therein in opposite directions and at such phase relation to each other as to balance out vibrating forces developed on said roller cutter means which are at right angles to said working direction of said roller cutter means.
 7. A work tool head according to claim 1 in which said mass means comprises three cylindrical masses in side by side relation in said roller cutter means with one mass rotating in one direction and the other two masses rotating in the opposite direction and with the phases of the masses being such that all vibrating forces developed on said roller cutter means which are at right angles to said working direction of said roller cutter means are balanced out.
 8. A work tool head according to claim 1 in which the natural frequencY of said mass means is approximately equal to the natural frequency of the weight of the roller cutter means and the bearing means therefor and the means suspending the roller cutter means from said carrier.
 9. A work tool head according to claim 1 in which said means supporting said bearing means on said carrier comprises an arm which at one end engages said bearing means and at the other end is supported on said carrier.
 10. A work tool head according to claim 9 in which said arm is a leaf spring and at said other end is fixed to said carrier.
 11. A work tool head according to claim 9 in which said arm at said other end is pivotally supported on said carrier on an axis parallel to the axis of rotation of said roller cutter means. 